Mike,
They all will work just fine for what you are wanting to do. I would get the most you can for your budget. Minimum 4-6gb memory and I recommend the i5. But i3 will do! If you were running something like SonarWiz that is graphics intensive and does simultaneous files and mosaics, then more memory and faster processor. But HumViewer and Dr Depth etc are not going to be that taxing on any of the newer systems.
I am never one for buying the absolute top of the line when it comes out in computers, but I never buy the lowest either. I also think you need to stick to brands that have a good record for quality prodcuts like ASUS and SONY.
Hope that helps.
Robert